Laura (Fox Noir). But if you are looking for one of his typical horror-centric movies, one of the Corman/Poe's (I like Pit & The Pendulum myself). Last Man On Earth (on the MGM double feature disc) is one his better performances. House On Haunted Hill (take the Warner over the public domain releases) is another favorite
For a good overview of his life and career check out "Laura." The disc includes a Vincent Price bio that provides a lot of great information. As for the movie, it features Price in a very different type of role than what he's usually remembered for.
I concur with CHAMPAGNE FOR CAESAR. Criterion was going to bring out Samuel Fuller's BARON OF ARIZONA with Price memorable as a real-life art forger, but I haven't heard anything recently about it.
All of the Corman Poes are terrific --- in fact, any of his AIP features from the sixties are wothwhile --- even "Dr. Goldfoot and The Bikini Machine".
His AIP/Corman films are terrific. House of Usher might be his best, not to mention it's an excellent adaptation. The Comedy of Terrors and The Raven are great, too. It's fun to see him not only act for comedy, but also among other greats like Karloff and Lorre. MGM's DVD's are quite good. I think Usher has a commentary by Roger Corman. All three films have great 16x9 2.35:1 remasters. The Pit and the Pendulum is on the B-side of a double feature re-issue of House of Usher, but it's not 16x9 like the other films.
While it's only on DVD in P&S and edited, his vocal performance as Zig-Zag for The Thief and the Cobbler is flawless (total ham and all dialogue is in verse).
It's funny you should mention Vincent. I Just recently started picking up some of the MGM double features including "The Pit and the Pendulum" and "Masque of the Red Death." I also just got the double feature of "The Fly" and "Return of the Fly." Also, don't forget the later career masterpieces of Dr. Phibes.
USHER is a great film, but, like the other films, it has almost nothing to do with Poe's story. I realized that for the first time a few months ago, after actually reading it. Note that the laserdisc features the original THE FALL OF THE HOUSE OF USHER onscreen title, while the DVD features HOUSE OF USHER as the onscreen title. The DVD of MASQUE OF THE RED DEATH is also missing snippets of footage that are intact on the LD. TALES OF TERROR is missing a color filter from a montage/dream sequence that is intact on the LD. The Corman Poe films have been a bit effed up on DVD in general.